Koa web app framework
Expressive HTTP middleware for node.js to make web applications and APIs more enjoyable to write. Koa's middleware stack flows in a stack-like manner, allowing you to perform actions downstream then filter and manipulate the response upstream. Koa's use of generators also greatly increases the readability and robustness of your application.
Only methods that are common to nearly all HTTP servers are integrated directly into Koa's small ~550 SLOC codebase. This includes things like content negotiation, normalization of node inconsistencies, redirection, and a few others.
Koa is not bundled with any middleware.
$ npm install koa
Koa is supported in node v4+ and node v0.12 with the
Koa v2 is currently in alpha. In this new version, the middleware function signature completely changes in favor of ES2015-2016 syntax:
// Koa application is now a class and requires the new operator.const app =// uses async arrow functionsappuseasync ctx next =>tryawait next // next is now a functioncatch errctxbody = message: errmessagectxstatus = errstatus || 500appuseasync ctx =>const user = await UsergetByIdctxsessionuserid // await instead of yieldctxbody = user // ctx instead of this
To learn more about Koa v2, follow this issue.
To try Koa v2,
npm install koa@next.
var koa = require'koa';var app = koa;// loggerappusevar start = ;yield next;var ms = - start;console.log'%s %s - %s' thismethod thisurl ms;;// responseappusethisbody = 'Hello World';;applisten3000;
$ make test